Production of conjugated diolefines



United States Patent PRODUCTION OF CONJUGATED DIOLEFINES John Habeshaw,Dollar, Wilfred John Oldham, Grangemouth, and Max Marin Wirth, Dollar,Scotland, as-

signors to British Hydrocarbon Chemicals Limited,

Devonshire House, Mayfair Place, Piccadilly, London,

England, a British company No Drawing. Filed Apr. 24, 1959, Ser. No.808,558 Claims priority, application Great Britain May 7, 1958 Claims.(Cl. 260-681) The present invention relates to the production ofconjugated diolefines by the reaction of aldehydes with mono-olefines.

The condensation of olefines with aldehydes is sometimes called thePrins reaction. Such condensation reactions are capable of yielding avariety of products such as m-dioxanes, unsaturated alcohols, 1:3 diolsor conjugated diolefines depending on the reaction conditions employed.The production of conjugated diolefines by the reaction betweenmono-olefines and aldehydes has been carried out by means of a two-stageprocess, and by a one-stage vapour phase process. A variety of catalystshas been proposed for use in the one-stage reaction of which the besthas appeared to be activated alumina. However, the yields of diolefineand efiiciency of conversion of the starting materials have been low,owing apparently to the tendency of the diolefine to react with thealdehyde forming higher boiling condensation products, and also becauseof the decomposition of formaldehyde to give products such as carbonmonoxide, so that the process has not represented an economicproposition on the industrial scale.

It is an object of the present application to provide a process for theproduction of conjugated diolefines by the condensation of aldehydes andolefines in a single stage reaction in which improved yields andefliciencies are obtained.

According to the present invention, the process for the production ofconjugated diolefines comprises reacting a lower mono-olefine withformaldehyde or acetaldehyde at an elevated temperature in the vapourphase in the presence as catalyst of a volatile acid, or a compoundwhich gives rise to such an acid under the reaction conditions, and asolid contact material.

As illustrative of the volatile acid catalysts which may be used in theprocess of the present invention may be mentioned volatile mineral acidssuch as hydrogen chloride, hydrogen iodide, and hydrogen bromide, andorganic acids such as formic, acetic, chloroacetic, trichloroacetic andtrifluoroacetic acids. It is preferred to use hydrogen chloride.Compounds giving rise under the reaction conditions to volatile acidsmay also be used. Such compounds include alkyl and ammonium halides suchas ammonium chloride, sec-butyl bromide, or preferably tertbutylchloride.

Any suitable solid contact material may be used in conjunction with theacid, such as silica gel, alumina, kieselguhr and pumice. The preferredsolid contact material is silica gel, which may, if desired, be treatedwith small amounts of a salt of a metal from group 2A or 2B of theperiodic table, such as calcium, barium, or cadmium.

The olefines which are suitable for use in the process of the presentinvention are the lower mono-olefines having up to six carbon atoms, andparticularly the tertiary olefines, i.e. olefines of the general formulaR R C=CHR where R and R are lower alkyl radicals, and R is hydrogen or alower alkyl radical. Olefines which isomerise under the reactionconditions to give tertiary olefines of the type R R C=CHR may also beused. It is particularly preferred to use isobutene, 2-methylbutene-2and 2-methylbutene-l. The molar proportion of olefine is preferably atleast equal to that of the aldehyde used, and is suitably between 1 and20 moles per mole of aldehyde.

The aldehydes which can be used in the process of the present inventionare formaldehyde and acetaldehyde. The use of formaldehyde is preferred.Advantageously the formaldehyde is derived from industrial formalinwhich is a solution of 36 to 40% by weight of formaldehyde in Water,usually containing some methanol. The formalin may be diluted withadditional water if desired. Suitably, the volatile acid catalyst iscombined with the formalin and the mixture is then vaporized and mixedwith the lower mono-olefine before passing over the contact material,and the steam in the gas mixture acts as a diluent. If desired inertdiluents may be used, such as nitrogen, carbon dioxide or hydrocarbonssuch as the lower parafi'ins. The proportion of inert diluent in thereaction gas mixture can vary widely, for instance between 0% and aboutby volume.

In a particularly preferred embodiment of the process of the presentinvention a mixture of lower mono-olefine with formaldehyde oracetaldehyde, and containing a proportion of hydrogen chloride, iscontinuously contacted at an elevated temperature in the vapour phasewith silica gel. The proportion of hydrogen chloride fed may varybetween moderately wide limits for instance between 0.01 and 10% byweight of the olefinic starting material.

The process of the present invention has the advantage that the usualinitial period of catalyst inefiiciency does not occur, or is verygreatly reduced. The process also produces a diolefine product ofappreciably higher purity than has been obtained in the processes usedhitherto. In particular, isoprene is made containing much lessmethylbutenes, which are diflicult and expensive to separate fromisoprene. The length of life of the solid contact material beforeregeneration is required is also greater than with many other solidcatalysts.

The reaction may be carried out over a wide range of temperatures, forinstance between and 400 C. The space velocity of the reactants over thesolid contact material may likewise vary and is suitably between 0.1 andS0 expressed as moles of aldehyde per litre of contact material perhour. The optimum velocity will vary depending on the reactiontemperature, and it is preferred to use the higher values of spacevelocities in the range set out with the higher temperatures, and viceversa.

For the process according to the invention the known methods of vapourphase catalysis may be employed. The solid contact material may be astationary or moving bed or a fluidized bed method may be used.

The diolefines can be recovered from the gaseous reaction product in anysuitable manner, for instance by condensing the product followed byfractional distillation of the resulting liquid mixture. 7 Unreactedolefines and formaldehyde can be recycled to the catalytic reaction.

A variety of conjugated diolefines can be produced by the process of theinvention, including isoprene, from isobutene and formaldehyde.

The diolefines made in accordance with this invention are valuablechemical intermediates, for instance in the preparation of syntheticrubbers.

The process of the invention is further illustrated with reference tothe following examples. r

-Example 1 A mixture of formaldehyde, steam and hydrogen chloride,derived from aqueous 18% formalin containing 2% by Weight ofhydrogen'chloride, and'isobutene was'passed in the vapour phase oversilica gel of 83 A. average pore diameter at atmospheric pressure and ata temperature of 300 C., the reaction products being condensed andfractionally distilled to recover the isoprene. Two processes werecarried out, the reaction conditions and results over the first 4 hoursbeing shown in Table 1, Runs A and B. The exceptional purity of theisoprene, which contained 4 Example 3 A mixture of formaldehyde, steamand ammonium chloride fed in the form of aqueous 18% formalin,containing one percent by weight of ammonium chloride, and

rn h

uc reduced amqums of methylbutenes compared Wlth 5 isobutene was reactedin the vapour phase as 111 Example for example, cracking catalysts, isnoteworthy.

2, the reaction cond1t1ons and results being shown in By way ofcomparison with the above example the proc- Table 3 ess was repeatedexcept that the hydrogen chloride was omitted from the formalin feed(Run C). No formation TABLE 3 of isoprene took place. Similarly, whenthe process was carried out in the presence of hydrogen chloride, but inthe C absence of silica gel, by passing the reactants through anCatalyst Silica gel/N114 1 empty tube (Run D), no isoprene was formed.(1) (2) TABLE 1 Space velocity, moles total feed/litre silica gel/hour56 G1 Mole ratio, isobutene/formaldehyde G. 1 5. 3 Formaldehydeconversion, percent l7 2!) Run No A B C D Efficiency of isopreneformation based on formal dehyde consumed, percent 4O Isoprene formationrate, g./litre silica gel/hour. 10 35 Catylyst Silica SilicaMethylbutenes content oflsoprene, weight percent. 0.5

gel H01 gel/H01 sum H01 1 20 gel (2) 1 4th hour. 2 Total first 4 hours.

a 1 Space velocity, moles total Ex mple 4 feed/M5111 36 37 150 141 38 12In this example trichloracetic acid was substituted in Male ratio,isobutene/formequimolar amounts for the hydrogen chloride used inaldehyde Examples 1A and 1B. The conditions and main resultsFormaldehyde conversion, are set out in Table 4, column (1) referring tothe results percent 69 70 43 1 12 from the fourth hour of operation andcolumn (2) to Efficiency of isoprene forresults from the total firstfour hours.

mation, based on formaldehydeconsumed,percent 45 41 36 40 Isopreneformation rate, g./ TABLE 4 litre silica gel/hour 63 61 127 152 Nil NilMethylbutenes content of 1 2 iscprene weight percent.. 1.0 0.3

Space velocity, moles total feed/litre silica gel/noun--. 73 74 1Results based on product from fourth hour of operation only. M018 M110lsoblltelle/fofmfildehyde 11111119 feed-u 3 0 a Results based on totalproduct from fir t four hou o a Formaldehyde conversion, percent 29 44Efiiciency of isoprene formation, based on formalde- I hyde refacted,perce1t1t ../1 t l Uh soprene ormation ra e g. ire si ice ge our Example2 Methylbutenes contentof isoprcne 0. 2

\A mixture of formaldehyde and steam derived from aqueous 18% formalinand isobutene containing 2 mol percent of butyl halide was passed in thevapour phase Example 5 gel of 33 average P dlametef at atmos" 45 Aseries of processes were carried out under the condi- Rherlc Pressure attemPel'atufe of reactions given in Example 1A. After four hours onstream tron products being condensed and fract onally distilledto h i1i1 carrier was regenerated by burning ff recover 1soprene. Two runs werecarried out, one using bon i a Stream f air at 500 0, f 1 1 Th run -WW611191156 and one 115mg y bmmlde, the was then resumed for a furtherfour hours and the rereactloll condltlons and results being shown InTable 2, 5O generation repeated. Results for successive four hour Runs Aand The Purity of the lsopl'ene Produced periods obtained in this wayare summarized in Table 5. which contained only very small amounts ofmethylbutenes, is noteworthy. The product contained less than TABLE 5 1%of alkyl halide based on the isoprene produced.

Number of regenerations Fresh 1 2 3 TABLE 2 Space velocity,moles/litre/hour 37 35 35 37 Mole ratio isobutene/formaldehyder 3.4 3.43.0 41 Run No A B Formaldehyde conversion, percent 70 66 52 47Eificiency of isoprene formation based on formaldehyde reacted, percent41 44 37 49 Catalyst Silica Isoprene formation rate g./litre/hour 61 6041 45 gel/tert. Silica Methylbutenes content of isoprcne product,

butyl gel/sec percent 1.0 1.1 0.9 1.3 chloride butyl bromide l 2 O O 65Example 6 Sptace velocity, moles total feed/litre silica gel] 76 74 5 Aseries of processes were carried out under the condi- Olll Mole ratio,isobutene/formaldehyde 4.4 4.1 4.1 nons of Example 1 A usmg slhca gelsamples of g q giglniialdehyge converfsion, percgnt. 50 37 35 physicalcharacteristics. Results are summarized in O m 011 386 011 0 El 5gniugitfifg lt j 54 49 45 T ble ,Wh1ch includes for comparison resultsunder cor- Isoprene formation rate g./litre silica gel/hour... 108 74 65Methylbutenescontent'ofisoprene, weight pefresponding conditions withpelleted diatomaceous earth cent... 0. 4 1. 0 and a commercialsilica/alumina catalyst which had been heat treated for 1 hour at 850 C.in the presence of 1 4th hour. steam. All the results reported refer tothe total of four 2 Total first four hours.

a Total fi st three hours, 75 hours operation with the catalyst.

TABLE 6 Catalyst carrier Silica gel Diat. Silicaearth alumina Surfacearea, sq. metres/g 330 626 655 465 282 207 189 30 114 Average porediameter A 83 22 36 55 111 109 140 88 Space velocity, moles/litre/hour.68 76 72 79 74 72 73 38 65 Mole ratio isobutene/formaldehyde 3.6 3.6 3.84.2 3.7 4.0 3.9 3.2 3.9 Formaldehyde conversion, percent- 60 39 37 48 4129 18 58 Isoprene formation efficiency, percent (based on formaldehydereacted) 50 48 45 61 59 62 41 15 42 Isoprene formation rateg./litre/hour 114 76 69 126 100 71 38 6 86 Methylbutenes content ofisoprene, percent 0. 1. 3 0. 4 0.4 0.1 0.1 0.1 0.4 3. 2

Example 7 TABLE 9 A series of processes were carried out in which 25milligram atoms of a group 2A or 2B metal were added Run i A B i O as anaqueous solution of the chlorides to the silica gel (40 g.) used ascarrier in the reaction. The products were ggggg g ggggggg 28 28 thendried at IOU-120 C. for 1 110111 and used as Cat- Isoprene formationefficiency, e6it"(55. i"6r1 alysts for the reaction at 300 C. andatmosph ric pres- 20 ,ggg ggg gggg gg gggel g? 3% sure, the formaldehydeand hydrogen chloride being fed Methylbutenes content oiisoprene pl2)(il 1 0i;::: 0.5 0.5 0.8 as an aqueous solution containing 18%formaldehyde and 2% of HCl. Other conditions and results are summarizedin Table 7, results with an untreated silica gel being included forcomparison. All results are for four hour periods starting with thefresh catalyst.

A series of processes were carried out at 300 C. and atmosphericpressure, as described in Example 1A using silica gel and hydrogenchloride as the catalyst. The total feed composition (mole fractions)was as follows:

Isobutene 0.640 Formaldehyde 0.080 HCl 0.004 Water-i-methanol (inaqueous formalin used as feed) 0.276v

The contact time (calculated from the volume of reactants at reactiontemperature) Was varied from 0.5 to 2.0 seconds in separate processes,with results shown in Table 8, all figures being for the fifth hour onstream of the catalyst.

TABLE 8 Run No A i B 0 Contact time, secs 0. 5 1. 0 2. 0 Formaldehydeconversion, percent. 35 49 64. 5 Isoprene formation efficiency, percent(based on formaldehyde consumed) 78.5 78. 5 64. 5 Isoprene formationrate g./litre/hour 230 160 90 Methylbutenes content of isoprene, percent0. 4 0. 5 0. 7

Example 9 Using the feed composition of the process of Example 7 aseries of processes were carried out in which the reaction temperatureWas varied, the contact time being 1.0 second and the pressureatmospheric. Results are summarized in Table 9, figures again referringto the fifth hour on stream.

Example 10 A series of processes were carried out at 300 C. andatmospheric pressure as described in Example 1A, with a total feedcontaining 0.64 and 0.08 mole fractions of isobutene and formaldehyderespectively. The mole fraction of HCl fed was varied, with resultsshown in Table 10, all figures again relating to the fifth hour ofoperation. The contact time was 1.0 second for all the tests.

We claim:

1. The process for the production of isoprene from isobutene andformaldehyde which comprises reacting the isobutene and formaldehyde atan elevated temperature between about and 400 C. in the vapor phase inthe presence of a catalyst consisting of the vapor of a hydrogen halideof the group hydrogen chloride, hydrogen bromide and hydrogen iodide andsilca gel as solid contact material.

2. The process for the production of isoprene from isobutene andformaldehyde which comprises reacting the isobutene and formaldehyde atan elevated temperature between about 100 and 400 C. in the vapor phasein the presence of hydrogen chloride vapor as catalyst and silica gel assolid contact material.

3. The process for the production of isoprene from isobutene andformaldehyde which comprises reacting the isobutene and formaldehyde atan elevated temperature between about 100 and 400 C. in the vapor phasein the presence, as catalyst, of the vapor of hydrogen chloride in theproportion of between 0.01 and 10% by weight based on the isobutenestarting material and silica gel as solid contact material.

4. The process for the production of isoprene from isobutene andformaldehyde which comprises reacting the isobutene and formaldehyde atan elevated temperature between about 250 and 350 C. in the vapor phasein the presence of hydrogen chloride vapor as catalyst and silica gel assolid contact material.

5. The process for the production of isoprene from isobutene andformaldehyde which comprises reacting References Cited in the file ofthis patent UNITED STATES PATENTS Friedrichsen et a1 Oct. 22, 1940Arundale et a1. June 6, 1944 Amos et al Dec. 25, 1945 Workman Dec. 17,1946

1. THE PROCESS FOR THE PRODUCTION OF ISOPRENE FROM ISOBUTENE ANDFORMADEHYDE WHICH COMPRISES REACTING THE ISOBUTENE FORMALDEHYDE AT ANELEVATED TEMPERATURE BETWEEN ABOUT 100* AND 400* C. IN THE VAPOR PHASEIN THE PRESENCE OF A CATALYST CONSISTING OF THE VAPOR OF A HYDROGENHALIDE OF THE GROUP HYDROGEN CHLORIDE, HYDROGEN BROMIDE AND NHYDROGENIODINE AND SILCA GEL AS SOLID CONTACT MATERIAL.